Regenerative cascaded H bridge power supply

ABSTRACT

For a power supply with a reduced number of semiconductor devices, a transformer receives a three-phase primary voltage and steps the three-phase primary voltage up or down to a secondary voltage with a plurality of secondary winding sets to a plurality of first phase voltages, a plurality of second phase voltages, and a plurality of third phase voltages. A plurality of power cell sets each include a plurality of power cells cascaded connected. Each power cell comprises a rectifier and an inverter. The rectifier includes two first active switches that are serially connected and receive a phase voltage at a first switch midpoint, two second active switches that are serially connected and receive another phase voltage at a second switch midpoint, and two capacitors that are serially connected and receive another phase voltage at a capacitor midpoint between the capacitors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of and claims priority toU.S. patent application Ser. No. 16/393,613 entitled “REDUCEDSEMICONDUCTOR DEVICE POWER CELL VOLTAGE DRIVE” and filed on Apr. 24,2019 for Zhong Y. Cheng, which is incorporated herein by reference.

BACKGROUND INFORMATION

subject matter disclosed herein relates to power supplies and moreparticularly to regenerative cascaded H bridge power supplies.

BRIEF DESCRIPTION

A power supply based on cascaded power cells with a reduced number ofsemiconductor devices is disclosed. The power supply includes atransformer and a plurality of power cell sets. The transformer receivesa three-phase primary voltage and steps the three-phase primary voltageup or down to a secondary voltage with a plurality of secondary windingsets to a plurality of first phase voltages, a plurality of second phasevoltages, and a plurality of third phase voltages. The plurality ofpower cell sets each comprise a plurality of power cells cascadedconnected. Each power cell comprises a rectifier and an inverter. Therectifier comprises two first active switches that are seriallyconnected and receive a phase voltage at a first switch midpoint, twosecond active switches that are serially connected and receive anotherphase voltage at a second switch midpoint, and two capacitors that areserially connected and receive another phase voltage at a capacitormidpoint between the capacitors. The two first active switches, thesecond two first active switches, and the two capacitors of each powercell are connected in parallel. An apparatus and a drive also performthe functions of the power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the embodiments of the invention will bereadily understood, a more particular description of the embodimentsbriefly described above will be rendered by reference to specificembodiments that are illustrated in the appended drawings. Understandingthat these drawings depict only some embodiments and are not thereforeto be considered to be limiting of scope, the embodiments will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings, in which:

FIG. 1A is a schematic diagram of a power supply according to anembodiment;

FIG. 1B is a schematic diagram of a power supply according to analternate embodiment;

FIG. 1C is a schematic diagram of power semiconductor devices accordingto an embodiment.

FIG. 2A is a schematic diagram of a power cell with a six-devicerectifier and a two-device inverter according to an embodiment;

FIG. 2B is a schematic diagram of a power supply with power cells with asix-device rectifier and a two-device inverter according to anembodiment;

FIG. 3A is a schematic diagram of a power cell with a six-devicerectifier and a two-device inverter according to an alternateembodiment;

FIG. 3B is a schematic diagram of a power supply with power cells with asix-device rectifier and a two-device inverter according to an alternateembodiment;

FIG. 4A is a schematic diagram of a power cell with a four-devicerectifier and a two-device inverter according to an embodiment;

FIG. 4B is a schematic diagram of a power supply with power cells with afour-device rectifier and a two-device inverter according to anembodiment;

FIG. 5A is a schematic diagram of a power cell with a four-devicerectifier and a two-device inverter according to an alternateembodiment;

FIG. 5B is a schematic diagram of a power supply with power cells with afour-device rectifier and a two-device inverter according to analternate embodiment;

FIG. 6A is a schematic diagram of a power cell with a two-devicerectifier and a four-device inverter according to an embodiment;

FIG. 6B is a schematic diagram of a power supply with power cells with atwo-device rectifier and a four-device inverter according to anembodiment;

FIG. 7A is a schematic diagram of a power cell with a two-devicerectifier and a four-device inverter according to an alternateembodiment;

FIG. 7B is a schematic diagram of a power supply with power cells with atwo-device rectifier and a four-device inverter according to analternate embodiment;

FIG. 8A is a schematic diagram of a power cell with a two-devicerectifier and a two-device inverter according to an embodiment;

FIG. 8B is a schematic diagram of a power supply with power cells with atwo-device rectifier and a two-device inverter according to anembodiment;

FIG. 9A is a schematic diagram of a power cell with a two-devicerectifier and a two-device inverter according to an alternateembodiment;

FIG. 9B is a schematic diagram of a power supply with power cells with atwo-device rectifier and a two-device inverter according to an alternateembodiment;

FIG. 10 is a flow chart diagram of a power supply method according to anembodiment;

FIG. 11 is graphs of power supply outputs according to an embodiment;

FIG. 12A is a schematic diagram of a power supply according to anembodiment;

FIG. 12B is a schematic diagram of an alternate power supply accordingto an embodiment;

FIG. 12C is a schematic diagram of an alternate power supply accordingto an embodiment;

FIG. 12D is a schematic diagram of an alternate power supply accordingto an embodiment;

FIG. 13A is a schematic diagram of an active switch according to anembodiment;

FIGS. 13B-D are schematic diagram of a power cell according to anembodiment;

FIGS. 14A-D are schematic diagrams of power cell switching according toan embodiment;

FIG. 15 is a graph of power cell phase voltages according to anembodiment;

FIG. 16 is a flow chart diagram of a power supply method according to analternate embodiment;

FIG. 17A is graphs of power supply harmonic spectrums according to anembodiment;

FIG. 17B is a graph of power supply output currents according to anembodiment;

FIG. 17C is graphs of power supply harmonic spectrums according to analternate embodiment;

FIG. 17D is a graph of power supply output currents according to analternate embodiment;

FIG. 17E are graphs of a motor speed profile and motor torque accordingto an embodiment;

FIG. 17F is a graph of a power supply harmonic spectrum according to anembodiment;

FIG. 17G is a graph of a power supply harmonic spectrum according to anembodiment;

FIG. 17H is a graph of a power supply harmonic spectrum according to analternate embodiment; and

FIG. 17I is a graph of a power supply harmonic spectrum according to analternate embodiment.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment, but mean “one or more but not all embodiments” unlessexpressly specified otherwise. The terms “including,” “comprising,”“having,” and variations thereof mean “including but not limited to”unless expressly specified otherwise. An enumerated listing of itemsdoes not imply that any or all of the items are mutually exclusiveand/or mutually inclusive, unless expressly specified otherwise. Theterms “a,” “an,” and “the” also refer to “one or more” unless expresslyspecified otherwise.

The schematic flowchart diagrams and/or schematic block diagrams in theFigures illustrate the architecture, functionality, and operation ofpossible implementations. It should also be noted that, in somealternative implementations, the functions noted in the block may occurout of the order noted in the Figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. Although various arrow types and line typesmay be employed in the flowchart and/or block diagrams, they areunderstood not to limit the scope of the corresponding embodiments.Indeed, some arrows or other connectors may be used to indicate only anexemplary logical flow of the depicted embodiment.

The description of elements in each figure may refer to elements ofproceeding figures. Like numbers refer to like elements in all figures,including alternate embodiments of like elements.

FIG. 1A is a schematic diagram of a power supply 100 a. The power supply100 a supplies a three-phase AC output with variable voltage andfrequency to the load. The AC output may drive one or more motors as theload. The power supply 100 a includes a phase shifting transformer 105and a plurality of power cell sets 115.

In the depicted embodiment, the phase shifting transformer 105 includesprimary winding 135, a core 140, and a plurality of secondary windingsets 130. The primary winding 135 of the phase shifting transformer 105receives the three-phase primary voltage. The plurality of secondarywinding sets 130 are magnetically coupled with the primary winding 135and step the three-phase primary voltage up or down to a secondaryvoltage. In one embodiment, there is phase shifting between thedifferent secondary winding sets 130. The transformer 105 is shown withDelta (Δ) connected primary winding 135 and zigzag connected secondarywinding sets 130. It can also be Wye (Y) connected primary winding 135and extended-Delta (Δ) secondary winding set 130, or polygon connectedsecondary winding set 130.

In the depicted embodiment, the phase shifting transformer 105 comprises9 secondary winding sets 130 with 20 degree phase shifts among thevoltage provided by the top three secondary winding sets 130 a, themiddle three secondary winding sets 130 b, and the bottom threesecondary winding sets 130 c as indicated in FIG. 1A. each secondarywinding set 130 provide the secondary voltage with the specified phaseto the power cell sets 115.

In this embodiment, an exemplary 9 power cells circuit is shown. Thenumber of power cells 110 may change depending on the requirement of theoutput voltage, thus the number of secondary winding sets 130 for eachpower cell set 115 will change accordingly. Generally speaking, the samecircuit topology can be used for any number n of power cells 110 inseries in each power cell set 115, and there will be the same amount ofsecondary winding sets 130 feeding each of the power cells 110. Thephase shifting angles shown in FIG. 1A is also exemplary for n=3. Theseangles can be changed. In general, for n secondary winding sets 130feeding n power cells 110 of each three-phase power cell set 115A-C, thephase shift angle within each set is 60°/n, or 20°/n. For example, ifn=4, the phase shift angle of the transformer secondary windings 130 foreach power cell set 115 is 60°/4=15°, or 20°/4=5°. If n=5, the phaseshift angle will be 60°/5=12°, or 20°/5=4°, and so on.

The plurality of power cell sets 115 each comprise a plurality of powercells 110 that are cascaded connected. Each power cell 110 receives oneof a single phase and a three-phase voltage of a distinct secondarywinding set 130 of the phase shifting transformer 105. Each power cellset 115 generates one phase 160A-C of a three-phase AC output.

The power cells 110 include a plurality of semiconductor devices torectify and invert the voltage received from a secondary winding set 130into a phase 160A-C of the three-phase AC output. As more semiconductordevices are used in the power cells 110, the cost and size of the powercells 110 and the power supply 100 a are increased. The embodimentsreduce the number of semiconductor devices in the power cells 110 and/orpower supply 100 to reduce the cost and size of the power supply 100. Inone embodiment, each power cell 110 comprises no more than eight powersemiconductor devices. The power supply 100 is organized to provide theAC output with the reduced number of power semiconductor devices,resulting in significant cost savings.

FIG. 1B is an exemplary schematic diagram of a power supply 100 b. Inthe depicted embodiment, the phase shifting transformer 105 comprises 3secondary winding sets 130 with 20-degree phase shifts among the voltageprovided each secondary winding set 130. It differs from FIG. 1A in thatthe three phase secondary winding sets are terminated in such way thatsingle phase power can be provided to the power cells, thus the numberof three-phase secondary windings is ⅓ comparing to FIG. 1A.

In this embodiment, an exemplary 9 power cells circuit is shown. Thenumber of power cells may change depending on the requirement of theoutput voltage, thus the number of secondary windings 130 for each powercell set 115 will change accordingly. Generally speaking, the samecircuit topology can be used for any number n of power cells 110 inseries in each power cell set 115, and there will be the same amount ofsecondary windings 130 feeding each of the power cells 110. The phaseshifting angles shown in FIG. 1A is also exemplary for n=3. These anglesmay be changed. In general, for n secondary windings 130 feeding n powercells 110 of each three-phase power cell set 115A-C, the phase shiftangle within each power cell set 115 is 60°/n. For example, if n=4, thephase shift angle of the transformer secondary windings 130 for eachpower cell set 115 is 60°/4=15°. If n=5, the phase shift angle will be60°/5=12°, and so on.

The topologies shown in FIG. 1A and FIG. 1B will be applied to the powercells depicted later. Exemplary n=3 power cells per set are used todemonstrate the circuit topology. In real implementation n can be anynatural number.

FIG. 1C is a schematic diagram of power semiconductor devices 125. Asused herein, a power semiconductor device 125 is one of a diode 125 aand an active switch 125 b. The diode 125 a may also be a thyristor, orother active semiconductor switches. The active switch 125 b may be anInsulated Gate Bipolar Transistor (IGBT) 125 b. In one embodiment, theactive switch 125 b is field effect transistor (FET) 125 b. The activeswitch 125 b may be a metal-oxide semiconductor field-effect transistor(MOSFET) 125 b or integrated gate commuted thyristor (IGCT). The activeswitch 125 b may be other semiconductor switching devices such assilicon controlled rectifiers (SCR). The quantity of semiconductorswitches is counted from circuit principle point of view. Semiconductordevices connected in parallel or series are count as single functionaldevice. Each active switch 125 b may comprise an anti-parallel diode143. A power cell 110 may have no more than eight power semiconductordevices 125. In one embodiment, the no more than eight powersemiconductor devices 125 are organized as a rectifier 150 and aninverter 155 within the power cell 110. The rectifier 150 mayselectively modify the direction of an input current. The inverter 155may form the required AC output. In one embodiment, a power cell 110includes additional non-power semiconductor devices such as capacitors,connectors, connections, and the like. The numbers of non-powersemiconductor devices may not be reduced.

FIG. 2A is a schematic diagram of a power cell 110-1 with a six-powersemiconductor device rectifier 150 and a two-power semiconductor deviceinverter 155. In the depicted embodiment, the power cell 110-1 comprisesa rectifier 150 and an inverter 155. The rectifier 150 comprises sixdiodes 125 a. The rectifier 150 is connected to one secondary windingset 130 ac 1-3. The inverter 155 comprises two IGBTs 125 b that output aphase of the three-phase AC output and a neutral 145N. Two non-powersemiconductor device capacitors 195 are also shown.

FIG. 2B is a schematic diagram of a power supply 100 a of FIG. 1A withpower cells 110-1 of FIG. 2A with a six-power semiconductor devicerectifier 150 and a two-power semiconductor device inverter 155. In thedepicted embodiment, each phase of the three-phases of the secondarywinding sets 130 comprises three multiphase sections 185. The rectifier150 of each power cell 110-1 comprises six diodes 125 a. The inverter155 of each power cell 110-1 comprises two IGBTs 125 b. For clarity, onepower cell set 115 is fully displayed and the two other power cell sets115 are schematically displayed.

FIG. 3A is a schematic diagram of a power cell 110-2 with a six-powersemiconductor device rectifier 150 and a two-power semiconductor deviceinverter 155. In the depicted embodiment, the power cell 110-2 comprisesa rectifier 150 and an inverter 155. The rectifier 150 comprises sixIGBTs 125 b. The rectifier 150 is connected to one secondary winding set130 ac 1-3. The inverter 155 comprises two IGBTs 125 b that output aphase 160A-C of the three-phase AC output and a neutral 145N. Twonon-power semiconductor device capacitors 195 are also shown.

FIG. 3B is a schematic diagram of a power supply 100 a of FIG. 1A withpower cells 110-2 of FIG. 3A with a six-semiconductor power devicerectifier 150 and a two-semiconductor power device inverter 155. Eachphase of the three-phases of the secondary winding sets 130 comprisesthree multiphase sections 185. The rectifier 150 of each power cell110-2 comprises six IGBTs 125 b. The inverter 155 of each power cell110-2 comprises two IGBTs 125 b. For clarity, one power cell set 115 isfully displayed and the two other power cell sets 115 are schematicallydisplayed.

FIG. 4A is a schematic diagram of a power cell 110-3 with afour-semiconductor power device rectifier 150 and a two-semiconductorpower device inverter 155. In the depicted embodiment, the power cell110-3 comprises a rectifier 150 and an inverter 155. The rectifier 150comprises four diodes 125 a. The rectifier 150 is connected to onesecondary winding set 130 ac 1-2. The inverter 155 comprises two IGBTs125 b that output a phase 160A-C of the three-phase AC output and aneutral 145N. Two non-power semiconductor device capacitors 195 are alsoshown.

FIG. 4B is a schematic diagram of a power supply 110 b of FIG. 1B withpower cells 110-3 of FIG. 4A with a four-semiconductor power devicerectifier 150 and a two-semiconductor power device inverter 155. Thephase shifting transformer 105 comprises 3 secondary winding sets 130with 20-degree phase shifts among the voltage provided each secondarywinding set 130. The rectifier 150 of each power cell 110-3 comprisesfour diodes 125 a. The inverter 155 of each power cell 110-3 comprisestwo IGBTs 125 b. For clarity, one power cell set 115 is fully displayedand the two other power cell sets 115 are schematically displayed.

FIG. 5A is a schematic diagram of a power cell 110-4 with afour-semiconductor power device rectifier 150 and a two-semiconductorpower device inverter 155. In the depicted embodiment, the power cell110-4 comprises a rectifier 150 and an inverter 155. The rectifier 150comprises four IGBTs 125 b. The rectifier 150 is connected to onesecondary winding set 130 ac 1-2. The inverter 155 comprises two IGBTs125 b that output a phase 160A-C of the three-phase AC output and aneutral 145N. Two non-power semiconductor device capacitors 195 are alsoshown.

FIG. 5B is a schematic diagram of a power supply 100 b of FIG. 1B withpower cells 110-4 of FIG. 5A with a four-semiconductor power devicerectifier 150 and a two-semiconductor power device inverter 155. In thedepicted embodiment, the rectifier 150 of each power cell 110-4comprises four IGBTs. The inverter 155 of each power cell 110-4comprises two IGBTs 125 b. In addition, each power cell 110-4 comprisesan LCL filter 15 that filters the current from the secondary winding set130. For clarity, one power cell set 115 is fully displayed and the twoother power cell sets 115 are schematically displayed.

FIG. 6A is a schematic diagram of a power cell 110-5 with atwo-semiconductor power device rectifier 150 and a four-semiconductorpower device inverter 155. In the depicted embodiment, the power cell110 comprises a rectifier 150 and an inverter 155. The rectifier 150comprises two diodes 125 a. The rectifier 150 is connected to onesecondary winding set 130 ac 1-2. The inverter 155 comprises four IGBTs125 b that output a phase 160A-C of the three-phase AC output and aneutral 145N. Two non-power semiconductor device capacitors 195 are alsoshown.

FIG. 6B is a schematic diagram of a power supply 100 b of FIG. 1B withpower cells 110-5 with a two-semiconductor power device rectifier 150and a four-semiconductor power device inverter 155. The rectifier 150 ofeach power cell 110-5 comprises two diodes 125 a. The inverter 155 ofeach power cell 110-5 comprises four IGBTs 125 b. For clarity, one powercell set 115 is fully displayed and the two other power cell sets 115are schematically displayed.

FIG. 7A is a schematic diagram of a power cell 110-6 with atwo-semiconductor power device rectifier 150 and a four-semiconductorpower device inverter 155. In the depicted embodiment, the power cell110-6 comprises a rectifier 150 and an inverter 155. The rectifier 150comprises two IGBTs 125 b. The rectifier 150 is connected to onesecondary winding set 130 ac 1-2. The inverter 155 comprises four IGBTs125 b that output a phase 160A-C of the three-phase AC output and aneutral 145N. Two non-power semiconductor device capacitors 195 are alsoshown.

FIG. 7B is a schematic diagram of a power supply 100 b of FIG. 1B withpower cells 110-6 of FIG. 7A with a two-semiconductor power devicerectifier 150 and a four-semiconductor power device inverter 155. In thedepicted embodiment, the rectifier 150 of each power cell 110-6comprises two IGBTs 125 b. The inverter 155 of each power cell 110-6comprises four IGBTs 125 b. In addition, each power cell 110-6 comprisesan LCL filter 15. For clarity, one power cell set 115 is fully displayedand the two other power cell sets 115 are schematically displayed.

FIG. 8A is a schematic diagram of a power cell 110-7 with atwo-semiconductor power device rectifier 150 and a two-semiconductorpower device inverter 155. In the depicted embodiment, the power cell110-7 comprises a rectifier 150 and an inverter 155. The rectifier 150comprises two diodes 125 a. The rectifier 150 is connected to onesecondary winding set 130 ac 1-2. The inverter 155 comprises two IGBTs125 b that output a phase 160A-C of the three-phase AC output and aneutral 145N. Two non-power semiconductor device capacitors 195 are alsoshown.

FIG. 8B is a schematic diagram of a power supply 100 b of FIG. 1B withpower cells 110-7 of FIG. 8A with a two-semiconductor power devicerectifier 150 and a two-semiconductor power device inverter 155. In thedepicted embodiment, the rectifier 150 of each power cell 110-7comprises two diodes 125 a. The inverter 155 of each power cell 110-7comprises two IGBTs 125 b. For clarity, one power cell set 115 is fullydisplayed and the two other power cell sets 115 are schematicallydisplayed.

FIG. 9A is a schematic diagram of a power cell 110-8 with atwo-semiconductor power device rectifier 150 and a two-semiconductorpower device inverter 155. In the depicted embodiment, the power cell110-8 comprises a rectifier 150 and an inverter 155. The rectifier 150comprises two IGBTs 125 b. The rectifier 150 is connected to onesecondary winding set 130 ac 1-2. The inverter 155 comprises two IGBTs125 b that output a phase 160A-C of the three-phase AC output and aneutral 145N. Two non-power semiconductor device capacitors 195 are alsoshown.

FIG. 9B is a schematic diagram of a power supply 100 b of FIG. 1B withpower cells 110-8 of FIG. 9A with a two-semiconductor power devicerectifier 150 and a two-semiconductor power device inverter 155. In thedepicted embodiment, the rectifier 150 of each power cell 110-8comprises two IGBTs 125 b, and the inverter 155 of each power cell 110comprises two IGBTs 125 b. In addition, each power cell 110-8 comprisesan LCL filter 15. For clarity, one power cell set 115 is fully displayedand the two other power cell sets 115 are schematically displayed.

FIG. 10 is a flow chart diagram of a power supply method 500. The method500 may be performed by the power supply 100. The method 500 may provide501 a phase shifting transformer 105 that receives the three-phaseprimary voltage and steps the three-phase primary voltage down to thesecondary voltage with a plurality of secondary winding sets 130 a-c. Inone embodiment, there is phase shifting between different secondarywinding sets 130.

The method may further provide 503 a plurality of power cell sets 115that each comprise a plurality of power cells 110 cascaded connected.Each power cell 110 may receive one of a single phase and a three-phasevoltage of a distinct secondary winding set 130 of the phase shiftingtransformer 105. Each power cell 110 may comprise no more than eightpower semiconductor devices 125 organized as a rectifier 150 and aninverter 155. Each power semiconductor device 125 may be one of a diode125 a and an IGBT 125 b. Each IGBT may comprise an anti-parallel diode143. Each power cell set 115 may generate one phase of a three-phase ACoutput.

FIG. 11 is graphs of power supply outputs that compares the line-to-lineoutput voltage 201, the line-to-line harmonics 203, the line-to-neutraloutput voltage 205, and the line-to-neutral current 207 for the outputof a prior art power cell, the power cell 110-1 of FIG. 2A, the powercell 110-3 of FIG. 4A, the power cell 110-5 of FIG. 6A, and the powercell 110-7 of FIG. 8A.

FIG. 12A is a schematic diagram of a power supply 100 c. The powersupply 100 c may be a cascade H bridge power supply 100 that supportsregeneration. The power supply 100 c supplies a three-phase AC output160 with variable voltage and frequency to a load such as the motor 123.The power supply 100 c includes a phase shifting transformer 105 and aplurality of power cell sets 115.

In the depicted embodiment, the phase shifting transformer 105 includesprimary winding 135, a core 140, and a plurality of 3k secondary windingsets 130, where k is an integer. The primary winding 135 of the phaseshifting transformer 105 receives the three-phase primary voltage. Theplurality of secondary winding sets 130 are magnetically coupled withthe primary winding 135 and step the three-phase primary voltage up ordown to a secondary voltage with the plurality of first phase voltages,the plurality of second phase voltages, and the plurality of third phasevoltages. The first, second, and third phase voltages are shownhereafter in FIGS. 13B-D.

In the depicted embodiment, the transformer 105 employs a Wye (Y)connected primary winding 135 and zigzag connected secondary windingsets 130. The transformer 105 may also employ a Delta (Δ) connectedprimary winding 135, an extended-Delta (Δ) secondary winding set 130,and/or polygon connected secondary winding sets 130.

The plurality of three power cell sets 115 each comprise a plurality ofpower cells 110 cascaded connected. Each power cell set 115 comprises kpower cells 110. Each power cell set 115 generates one phase of athree-phase AC output 160A-C. In the depicted embodiment, the phaseshifting transformer 105 comprises 3k secondary winding sets 130 andthree power cell rows 113-1-k. In one embodiment, the secondary phaseshift δ is

$\delta = \frac{60}{k}$degrees between the secondary winding sets 130 for each power cell set115. For example, for k=5, δ₁=+24 degrees, δ₂=+12 degrees, δ₃=0 degrees,δ₄=−12 degrees, δ₅=−24 degrees.

The power cells 110 may be controlled by the controller 127 withsinusoidal pulse width modulation control signals. In one embodiment,the power cells 110 are controlled with modulation control signalsselected from the group consisting of sinusoidal pulse width modulationcontrol signals, modified pulse width modulation control signals, randompulse width modulation control signals, third harmonic injection pulsewidth modulation control signals, and space vector modulation controlsignals. The carrier angle phase shifts θ may be the same for therectifier 150 in all power cells 110, θ₁=θ₂=θ₃ and the switchingfrequency for the modulation control signals is 4020 Hz. Alternatively,the carrier phase shifting angles of the rectifiers 150 in the powercell sets 115 may be shifted by 120 degrees from each other. Forexample, the carrier angles may be θ₁, θ₂=θ₁±120°, and θ₃=θ₁±240°. In acertain embodiment, the switching frequency for the modulation controlsignals is 1980 Hz.

FIG. 12B is a schematic diagram of a power supply 100 d. The powersupply 100 d may be a cascade H bridge power supply 100 that supportsregeneration. The power supply 100 d supplies a three-phase AC output160 with variable voltage and frequency to a load. In the depictedembodiment, the load is a motor 123. The AC output 160 may drive one ormore motors 123 as the load. The power supply 100 d includes a phaseshifting transformer 105 and a plurality of power cell sets 115.

In the depicted embodiment, the phase shifting transformer 105 includesprimary winding 135, a core 140, and a plurality of secondary windingsets 130. The primary winding 135 of the phase shifting transformer 105receives the three-phase primary voltage. The plurality of secondarywinding sets 130 are magnetically coupled with the primary winding 135and step the three-phase primary voltage up or down to a secondaryvoltage with a plurality of first phase voltages, a plurality of secondphase voltages, and a plurality of third phase voltages.

In the depicted embodiment, the transformer 105 employs a Wye (Y)connected primary winding 135 and zigzag connected secondary windingsets 130. The transformer 105 may also employ a Delta (Δ) connectedprimary winding 135, an extended-Delta (Δ) secondary winding set 130,and/or polygon connected secondary winding sets 130.

The plurality of power cell sets 115 each comprise a plurality of powercells 110 cascaded connected. Each power cell set 115 generates onephase of a three-phase AC output 160A-C. In the depicted embodiment, thephase shifting transformer 105 comprises 9 secondary winding sets 130and three power cell rows 113-1-3. In one embodiment, there is secondaryphase shifting between the different secondary winding sets 130. Thesecondary phase δ shifting may be 20 degrees. For example, δ₁=+20degrees, δ₂=0 degrees, δ₃=−20 degrees.

The power cells 110 may be controlled by a controller 127 withsinusoidal pulse width modulation control signals. In one embodiment,the power cells 110 are controlled with modulation control signalsselected from the group consisting of sinusoidal pulse width modulationcontrol signals, modified pulse width modulation control signals, randompulse width modulation control signals, third harmonic injection pulsewidth modulation control signals, and space vector modulation controlsignals. The carrier angle phase shifts θ may be the same for therectifier 150 in all power cells 110, θ₁=θ₂=θ₃ and the switchingfrequency for the modulation control signals is 4020 Hz. Alternatively,the carrier angles θ₁, θ₂, and θ₃ for rectifier 150 in the power cells110-1, 110-2, and 110-3 may be phase shifted by 120 degrees. Forexample, the carrier angles may be θ₁, θ₂=θ₁+120 degrees, and θ₃=θ₁+240degrees. In a certain embodiment, the switching frequency for themodulation control signals is 1980 Hz.

FIG. 12C is a schematic diagram of a power supply 100 e. The powersupply 100 e may be a cascade H bridge power supply 100 that supportsregeneration. The power supply 100 e supplies a three-phase AC output160 with variable voltage and frequency to a load such as the motor 123.The power supply 100 e includes a phase shifting transformer 105 and aplurality of power cell sets 115.

In the depicted embodiment, the phase shifting transformer 105 includesprimary winding 135, a core 140, and a plurality of 3k secondary windingsets 130, where k is an integer. The primary winding 135 of the phaseshifting transformer 105 receives the three-phase primary voltage. Theplurality of secondary winding sets 130 are magnetically coupled withthe primary winding 135 and step the three-phase primary voltage up ordown to a secondary voltage with the plurality of first phase voltages,the plurality of second phase voltages, and the plurality of third phasevoltages.

In the depicted embodiment, the transformer 105 employs a Wye (Y)connected primary winding 135 and zigzag connected secondary windingsets 130. The transformer 105 may also employ a Delta (Δ) connectedprimary winding 135 and/or and extended-Delta (Δ) secondary winding set130, and/or polygon connected secondary winding sets 130.

The plurality of three power cell sets 115 each comprise a plurality ofpower cells 110 cascaded connected. Each power cell set 115 comprises kpower cells 110. Each power cell set 115 generates one phase of athree-phase AC output 160A-C. In the depicted embodiment, the phaseshifting transformer 105 comprises 3k secondary winding sets 130 and kpower cell rows 113-1-k. In one embodiment, there is no secondary phaseshifting δ between the secondary winding sets 130, and δ₁=δ₂= . . .=δ_(k).

The power cells 110 may be controlled by the controller 127 withsinusoidal pulse width modulation control signals. In one embodiment,the power cells 110 are controlled with modulation control signalsselected from the group consisting of sinusoidal pulse width modulationcontrol signals, modified pulse width modulation control signals, randompulse width modulation control signals, third harmonic injection pulsewidth modulation control signals, and space vector modulation controlsignals. The carrier angles θ for the rectifiers 150 in each power cellrow 113-n may be the same. For example, the carrier angles a first row113-1 may be θ₁ degrees. The carrier phase shifting angles θ₁, θ₂, . . ., θ_(k) of rectifiers 150 in different power cell rows 113 may beshifted by

$\frac{360}{k}$degrees from each other. For example, for k=5, the carrier phaseshifting angles are θ₁, θ₂=θ₁+62 degrees, θ₃=θ₁+124 degrees, θ₄=θ₁−62degrees, θ₅=θ₁−124 degrees. For k=3, the carrier angles are θ₁ for thefirst power cell row 113-1, θ₂=θ₁±120° for the second power cell row113-2, and θ₃=θ₁±240° for the third power cell row 113-3. In a certainembodiment, the switching frequency for the modulation control signalsis 1980 Hz.

FIG. 12D is a schematic diagram of a power supply 100 f. The powersupply 100 f may be a cascade H bridge power supply 100 that supportsregeneration. The power supply 100 f supplies a three-phase AC output160 with variable voltage and frequency to a load such as the motor 123.The power supply 100 f includes a phase shifting transformer 105 and aplurality of power cell sets 115.

In the depicted embodiment, the phase shifting transformer 105 includesprimary winding 135, a core 140, and a plurality of secondary windingsets 130. The primary winding 135 of the phase shifting transformer 105receives the three-phase primary voltage. The plurality of secondarywinding sets 130 are magnetically coupled with the primary winding 135and step the three-phase primary voltage up or down to a secondaryvoltage with the plurality of first phase voltages, the plurality ofsecond phase voltages, and the plurality of third phase voltages.

In the depicted embodiment, the transformer 105 employs a Wye (Y)connected primary winding 135 and zigzag connected secondary windingsets 130. The transformer 105 may also employ a Delta (Δ) connectedprimary winding 135, an extended-Delta (Δ) secondary winding set 130,and/or polygon connected secondary winding sets 130.

The plurality of power cell sets 115 each comprise a plurality of powercells 110 cascaded connected. Each power cell set 115 generates onephase of a three-phase AC output 160A-C. In the depicted embodiment, thephase shifting transformer 105 comprises 9 secondary winding sets 130and three power cell rows 113-1-3. In one embodiment, there is nosecondary phase shifting δ between the top, middle, and bottom secondarywinding sets 130, and δ₁=δ₂=δ₃.

The power cells 110 may be controlled by the controller 127 withsinusoidal pulse width modulation control signals. In one embodiment,the power cells 110 are controlled with modulation control signalsselected from the group consisting of sinusoidal pulse width modulationcontrol signals, modified pulse width modulation control signals, randompulse width modulation control signals, third harmonic injection pulsewidth modulation control signals, and space vector modulation controlsignals. The carrier angles for the rectifiers 150 in power cell rows113 may be θ₁ for the first power cell row 113-1, θ₂=θ₁±120° for thesecond power cell row 113-2, and θ₃=θ₁±240° for the third power cell row113-3 and the switching frequency for the modulation control signals is1980 Hz.

FIG. 13A is a schematic diagram of an active switch 125 b. In thedepicted embodiment, the active switch 125 b includes an anti-paralleldiode 143. The active switch 125 b is controlled by a modulation controlsignal 129 from the controller 127.

FIGS. 13B-D are schematic diagram of a power cell 110. Each power cell110 comprises a rectifier 150 and an inverter 155. In the depictedembodiment, the inverter 155 is an H-bridge of four active switches 125b. The inverter 155 outputs a phase of the AC output 160 and connects tothe neutral 145.

The rectifier 150 comprising two first active switches 125 b-1 that areserially connected and receive a phase voltage 131 at a first switchmidpoint 133-1, two second active switches 125 b-2 that are seriallyconnected and receive another phase voltage 131 at a second switchmidpoint 133-2, and two capacitors 195 that are serially connected andreceive another phase voltage 131 at a capacitor midpoint 133-3 betweenthe capacitors 195, wherein the two first active switches 125 b-1, thesecond two first active switches 125 b-2, and the two capacitors 195 ofeach power cell 110 are connected in parallel. The distribution of phasevoltages 131 at the first switch midpoint 133-1, the second switchmidpoint 133-2, and the capacitor midpoint 133-3 reduces harmonics of aprimary current harmonic spectrum as is shown hereafter.

In FIG. 13B, a first power cell 110-1 is shown. A second phase voltage131-2 is connected to the first switch midpoint 133-1, a third phasevoltage 131-3 is connected to the second switch midpoint 133-2, and afirst phase voltage 131-1 is connected to the capacitor midpoint 133-3.In FIG. 13C, the third phase voltage 131-3 is connected to the firstswitch midpoint 133-1, the first phase voltage 131-1 is connected to thesecond switch midpoint 133-2, and the second phase voltage 131-2 isconnected to the capacitor midpoint 133-3 for a second power cell 110-2.In FIG. 13D, the first phase voltage 131-1 is connected to the firstswitch midpoint 133-1, the second phase voltage 131-2 is connected tothe second switch midpoint 133-2, and the third phase voltage 131-3 isconnected to the capacitor midpoint 133-3 for a third power cell 110-3.In one embodiment, the connections are employed for the power supplies100 e/100 f of FIGS. 12C-D and for some embodiments for the powersupplies 100 c/100 d of FIGS. 12 A-B.

The power cells 110 in the power supplies 100 c/100 d of FIGS. 12 A and12B may be connected to the secondary winding sets as follows: For thefirst power cells 110-1, the first switch midpoint 133-1 receives thesecond phase voltage 131-2 from an av secondary winding set 130-av, thesecond switch midpoint 133-2 receives the third phase voltage 131-3 froman aw secondary winding set 130-aw, and the capacitor midpoint 133-3receives the first phase voltage 131-1 from an au secondary winding set130-au. For the second power cells 110-2, the first switch midpoint133-1 receives the third phase voltage 131-3 from a bw secondary windingset 130-bw, the second switch midpoint 133-2 receives the first phasevoltage 131-1 from a bu secondary winding set 130-bu, and the capacitormidpoint 133-3 receives the second phase voltage 131-2 from a bysecondary winding set 130-bv. For the third power cells 110-3, the firstswitch midpoint 133-1 receives the first phase voltage 131-1 from a cusecondary winding set 130-cu, the second switch midpoint 133-2 receivesthe second phase voltage 131-2 from a cv secondary winding set 130-cv,and the capacitor midpoint 133-3 receives the third phase voltage 131-3from a cw secondary winding set 130-cw. The embodiments includeelectrical equivalents. The power cells 110 may be connected to thesecondary winding sets 130 as shown in Table 1 for FIG. 12B and FIG. 12Afor k=3.

TABLE 1 Secondary Winding Output 130 Power Cell 110 Phase Voltage 131130-av 110-1 133-1 130-aw 110-1 133-2 130-au 110-1 133-3 130-bw 110-2133-1 130-bu 110-2 133-2 130-bv 110-2 133-3 130-cu 110-3 133-1 130-cv110-3 133-2 130-cw 110-3 133-3

In one embodiment, for the power supplies 100 c and 100 d of FIGS. 12Aand 12B, for all power cells 110, the first switch midpoint 133-1, thesecond switch midpoint 133-2, and the third switch midpoint 133-3 areconnected in a same phase sequence. The embodiments include electricalequivalents.

In one embodiment, the power cells 110 in the power supplies 100 c/100 dof FIGS. 12A and 12B are connected to the secondary winding sets asfollows: The first switch midpoint 133-1 receives the same phase voltage131-1 from a u secondary winding set 130-un, the second switch midpoint133-2 receives the second phase voltage 131-2 from a v secondary windingset 130-vn, and the capacitor midpoint 133-3 receives the third phasevoltage 131-3 from a w secondary winding set 130-wn. The power cells 110may be connected to the secondary winding sets 130 as shown in Table 2for the power supply 100 of FIG. 12B and for FIG. 12A for k=3.

TABLE 2 Secondary Winding Output 130 Power Cell 110 Phase Voltage 131130-au 110-1 133-1 130-av 110-1 133-2 130-aw 110-1 133-3 130-bu 110-2133-1 130-bv 110-2 133-2 130-bw 110-2 133-3 130-cu 110-3 133-1 130-cv110-3 133-2 130-cw 110-3 133-3

The power cells 110 in the power supply 100 of FIG. 12A may be connectedto the secondary winding sets as follows: For a power cell row 113-x,where x=3L−2 for L is integer and L=1 to the upper integer limit of

$\left( \frac{k}{3} \right),$the first switch midpoint 133-1 receives the second phase voltage 131-2from an av secondary winding set 130-av, the second switch midpoint133-2 receives the third phase voltage 131-3 from an aw secondarywinding set 130-aw, and the capacitor midpoint 133-3 receives the firstphase voltage 131-1 from an au secondary winding set 130-au, for a powercell row 113-y. Where y is integer equals to x+1 and ranges from 2 to k,the first switch midpoint 133-1 receives the third phase voltage 131-3from a bw secondary winding set 130-bw, the second switch midpoint 133-2receives the first phase voltage 131-1 from a bu secondary winding set130-bu, and the capacitor midpoint 133-3 receives the second phasevoltage 131-2 from a by secondary winding set 130-bv, and for a powercell row 113-z. Where z is integer equals to x+2 and ranges from 3 to k,the first switch midpoint 133-1 receives the first phase voltage 131-1from a cu secondary winding set 130-cu, the second switch midpoint 133-2receives the second phase voltage 131-2 from a cv secondary winding set130-cv, and the capacitor midpoint 133-3 receives the third phasevoltage 131-3 from a cw secondary winding set 130-cw. In one embodiment,k=5, x=1, 4, y=2, 5, and z=3. The embodiments include electricalequivalents.

In one embodiment, for a power cell row 113-1 in the power supplies 100c/100 d in FIG. 12A (for k=3) and FIG. 12B, the first switch midpoint133-1 receives the second phase voltage 131-2 from an av secondarywinding set 130-av, the second switch midpoint 133-2 receives the thirdphase voltage 131-3 from an aw secondary winding set 130-aw, and thecapacitor midpoint 133-3 receives the first phase voltage 131-1 from anau secondary winding set 130-au, for a power cell row 113-2, the firstswitch midpoint 133-1 receives the third phase voltage 131-3 from a bwsecondary winding set 130-bw, the second switch midpoint 133-2 receivesthe first phase voltage 131-1 from a bu secondary winding set 130-bu,and the capacitor midpoint 133-3 receives the second phase voltage 131-2from a by secondary winding set 130-bv, and for a power cell row 113-3,the first switch midpoint 133-1 receives the first phase voltage 131-1from a cu secondary winding set 130-cu, the second switch midpoint 133-2receives the second phase voltage 131-2 from a cv secondary winding set130-cv, and the capacitor midpoint 133-3 receives the third phasevoltage 131-3 from a cw secondary winding set 130-cw. The power cells110 may be connected to the secondary winding sets 130 as shown in Table3 for the power supply 100 of FIG. 12B and for FIG. 12A for k=3.

TABLE 3 Secondary Winding Output 130 Power Cell 110 Phase Voltage 131130-av 113-1 133-1 130-aw 113-1 133-2 130-au 113-1 133-3 130-bw 113-2133-1 130-bu 113-2 133-2 130-bv 113-2 133-3 130-cu 113-3 133-1 130-cv113-3 133-2 130-cw 113-3 133-3

The power cells 110 in the power supply 100 e/100 f of FIGS. 12C and 12Dmay be connected to the secondary winding sets as follows. For firstpower cells 110-1, the first switch midpoint 133-1 receives the secondphase voltage 131-2 from an av secondary winding set 130-av, the secondswitch midpoint 133-2 receives the third phase voltage 131-3 from an awsecondary winding set 130-aw, and the capacitor midpoint 133-3 receivesthe first phase voltage 131-1 from an au secondary winding set 130-au.For second power cells 110-2, the first switch midpoint 133-1 receivesthe third phase voltage 131-3 from a bw secondary winding set 130-bw,the second switch midpoint 133-2 receives the first phase voltage 131-1from a bu secondary winding set 130-bu, and the capacitor midpoint 133-3receives the second phase voltage 131-2 from a by secondary winding set130-bv. For third power cells 110-3, the first switch midpoint 133-1receives the first phase voltage 131-1 from a cu secondary winding set130-cu, the second switch midpoint 133-2 receives the second phasevoltage 131-2 from a cv secondary winding set 130-cv, and the capacitormidpoint 133-3 receives the third phase voltage 131-3 from a cwsecondary winding set 130-cw.

The power cells 110 may be connected to the secondary winding sets 130as shown in Table 4 for the power supply 100 e of FIG. 12C (for k=3) andthe power supply 100 f of FIG. 12D.

TABLE 4 Secondary Winding Output 130 Power Cell 110 Phase Voltage 131130-av 110-1 133-1 130-aw 110-1 133-2 130-au 110-1 133-3 130-bw 110-2133-1 130-bu 110-2 133-2 130-bv 110-2 133-3 130-cu 110-3 133-1 130-cv110-3 133-2 130-cw 110-3 133-3

FIGS. 14A-D are schematic diagrams of power cell switching. Thecontroller 127 controls the modulation control signals 129 so that theactive switches 125 are switched. FIG. 14A shows a first position withactive switch 125-11 and active switch 125-22 on and active switch125-12 and active switch 125-21 off. FIG. 14B shows a second positionwith active switch 125-11 and active switch 125-21 on and active switch125-12 and active switch 125-22 off. FIG. 14C shows a third positionwith active switch 125-12 and active switch 125-21 on and active switch125-11 and active switch 125-22 off. FIG. 14D shows a fourth positionwith active switch 125-12 and active switch 125-22 on and active switch125-11 and active switch 125-21 off.

FIG. 15 is a graph of power cell phase voltages 121 for the power cellswitching of FIGS. 14A-D. The switching results in two oppositedirect/quadrature vectors 121 that are equal in magnitude and 180degrees out of phase. Phase voltage 121-1 is for the power cellswitching of FIG. 14A, phase voltage 121-2 is for the power cellswitching of FIG. 14B, phase voltage 121-3 is for the power cellswitching of FIG. 14C, and phase voltage 121-4 is for the power cellswitching of FIG. 14D. In one embodiment, there is no zero phase voltagevector.

FIG. 16 is a flow chart diagram of a power supply method 510. The method510 provides power to a load such as the motor 123 and may be performedby the power supply 100. The method 410 may provide 511 a transformer105 that receives a three-phase primary voltage and steps thethree-phase primary voltage up or down to a secondary voltage with aplurality of secondary winding sets 130 to a plurality of first phasevoltages 131-1, a plurality of second phase voltages 131-2, and aplurality of third phase voltages 131-3.

The method 510 further provides 513 a plurality of power cell sets 115that each comprise a plurality of power cells 110 cascaded connected.Each power cell 110 comprises a rectifier 150 and an inverter 155. Therectifier 150 comprises two first active switches 125 b-1 that areserially connected and receive a phase voltage 131 at a first switchmidpoint 133-1, two second active switches 125 b-2 that are seriallyconnected and receive another phase voltage 131 at a second switchmidpoint 133-2, and two capacitors 195 that are serially connected andreceive another phase voltage 131 at a capacitor midpoint 133-3 betweenthe capacitors 195. The two first active switches 125 b-1, the secondtwo first active switches 125 b-2, and the two capacitors 195 of eachpower cell 110 are connected in parallel.

FIG. 17A is a graph of power supply harmonic spectrums for the powersupply 100 of FIG. 12B. The switching frequency is 4020 Hz with theconnections of Table 1. The carrier angles are the same for therectifiers 150 in all power cells 110. The secondary currents harmonicspectrum for the secondary winding sets 130 and the primary currentsharmonic spectrum for the primary winding 135 are shown as magnitudes601 expressed as a percentage to the fundamental harmonic. The totalharmonic distortion (THD) is also specified.

FIG. 17B is graphs of power supply output currents Ia, Ib, and Ic forthe AC outputs 160 of the power supply 100 of FIG. 12B. The currents 603are measured per unit.

FIG. 17C is graphs of power supply harmonic spectrums for the powersupply 100 of FIG. 12B. The switching frequency is 4020 Hz with theconnections of Table 2. The carrier angles are the same for therectifiers 150 in all power cells 110. The secondary currents harmonicspectrum for the secondary winding sets 130 and the primary currentsharmonic spectrum for the primary winding 135 are shown as magnitudes601 expressed as a percentage to the fundamental harmonic. The THD isalso specified.

FIG. 17D is a graph of power supply output currents Ia, Ib, and Ic forthe AC outputs 160 of the power supply 100 of FIG. 12B. The currents 603are measured per unit.

FIG. 17E are graphs of a motor speed profile and motor torque for themotor 123 of FIG. 12B. The speed 607 measured in per unit and torque 609measured in per unit are shown while motoring and during regenerationover a time interval.

FIG. 17F is a graph of a power supply harmonic spectrum for the powersupply 100 of FIG. 12D during motoring. In the depicted embodiment, theswitching frequency is 1980 Hz, the connection of table 4 is used, andthe carrier angles for the rectifiers 150 in the power cell rows113-1/2/3 are shifted by 120 degrees. The primary current harmonicspectrum for the primary winding 135 is shown as magnitudes 601expressed as a percentage to the fundamental harmonic. The THD is alsospecified.

FIG. 17G is a graph of a power supply harmonic spectrum for the powersupply 100 of FIG. 12D during regeneration. In the depicted embodiment,the switching frequency is 1980 Hz, the connection of table 4 is used,and the carrier angles for the rectifiers 150 in the power cell rows113-1/2/3 are shifted by 120 degrees. The primary current harmonicspectrum for the primary winding 135 is shown as magnitudes 601expressed as a percentage to the fundamental harmonic. The THD is alsospecified.

FIG. 17H is a graph of a power supply harmonic spectrum for the powersupply 100 of FIG. 12B during motoring. The switching frequency is 1980Hz, the connections of Table 3 are used, and the carrier angles for therectifiers 150 in the power cells 110-1/2/3 are shifted by 120 degrees.The primary current harmonic spectrum for the primary winding 135 isshown as magnitudes 601 expressed as a percentage to the fundamentalharmonic. The THD is also specified.

FIG. 17I is a graph of a power supply harmonic spectrum for the powersupply 100 of FIG. 12B during regeneration. The switching frequency is1980 Hz, the connections of Table 3 are used, and the carrier angles forthe rectifiers 150 in the power cells 110-1/2/3 are shifted by 120degrees. The primary current harmonic spectrum for the primary winding135 is shown as magnitudes 601 expressed as a percentage to thefundamental harmonic. The THD is also specified.

Problem/Solution

The cost of a cascaded H bridge power supply 100 is significantlyimpacted by the number of power semiconductor devices 125 such as activeswitches 125 b in each power cell 110. A cascaded H bridge power supply100 may typically have at least six active switches 125 b in therectifier 150. Reducing the power semiconductor devices 125significantly reduces the cost of the power supply 100. The embodimentsemploy power cells 110 with reduced active switches 125 b in therectifier 150. As a result, the embodiments enable regenerative powersupplies 100 with significantly reduced cost.

This description uses examples to disclose the invention and also toenable any person skilled in the art to practice the invention,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the invention is definedby the claims and may include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal language of theclaims.

What is claimed is:
 1. A power supply comprising: a transformer thatreceives a three-phase primary voltage and steps the three-phase primaryvoltage up or down to a secondary voltage with a plurality of secondarywinding sets to a plurality of first phase voltages, a plurality ofsecond phase voltages, and a plurality of third phase voltages; and aplurality of power cell sets that each comprise a plurality of powercells cascaded connected, wherein each power cell comprises a rectifierand an inverter, the rectifier comprising two first active switches thatare serially connected and receive a phase voltage from a firstsecondary winding of a given secondary winding set at a first switchmidpoint, two second active switches that are serially connected andreceive another phase voltage from a second secondary winding of thegiven winding set at a second switch midpoint, and two capacitors inparallel with the rectifier and the inverter that are serially connectedand receive another phase voltage from a third secondary winding of thegiven secondary winding set at a capacitor midpoint between thecapacitors, wherein the two first active switches, the two second activeswitches, and the two capacitors of each power cell are connected inparallel.
 2. The power supply of claim 1, wherein the active switchesare switched as a first position with a first top active switch andsecond bottom active switch on, a second position with first top activeswitch and a second top active switch on, a third position with a secondbottom active switch and second top active switch on, and a first bottomfourth position with active switch and second bottom active switch on.3. The power supply of claim 1, wherein the inverter is an H-bridge offour active switches.
 4. The power supply of claim 1, wherein thetransformer comprises a primary winding, three power cell sets, and 3ksecondary winding sets, a secondary phase shift is$\delta = \frac{60}{k}$ degrees between the secondary winding sets foreach power cell set, and each power cell set comprises k power cells,wherein k is in integer.
 5. The power supply of claim 4, wherein forfirst power cells, the first switch midpoint receives the second phasevoltage from an (av) secondary winding set, the second switch midpointreceives the third phase voltage from an (aw) secondary winding set, andthe capacitor midpoint receives the first phase voltage from an (au)secondary winding set, for second power cells, the first switch midpointreceives the third phase voltage from a (bw) secondary winding set, thesecond switch midpoint receives the first phase voltage from a (bu)secondary winding set, and the capacitor midpoint receives the secondphase voltage from a (bv) secondary winding set, and for third powercells, the first switch midpoint receives the first phase voltage from a(cu) secondary winding set, the second switch midpoint receives thesecond phase voltage from a (cv) secondary winding set, and thecapacitor midpoint receives the third phase voltage from a (cw)secondary winding set.
 6. The power supply of claim 5, wherein k=3, theswitching frequency is 4020 Hertz (Hz), the power cells are controlledwith sinusoidal pulse width modulation control signals, and the carrierangle phase shifts are the same for the rectifiers in all power cells.7. The power supply of claim 4, wherein for all power cells, the firstswitch midpoint, the second switch midpoint, and the third switchmidpoint are connected in a same phase sequence.
 8. The power supply ofclaim 7, wherein k=3, the switching frequency is 4020 Hz., and in allpower cells the power cells, the first switch midpoint receives the samephase voltage from a u secondary winding set, the second switch midpointreceives the second phase voltage from a v secondary winding set, andthe capacitor midpoint receives the third phase voltage from a wsecondary winding set, the power cells are controlled with sinusoidalpulse width modulation control signals, and carrier angle phase shiftsare the same for the rectifiers.
 9. The power supply of claim 4, whereinthere are k power cell rows, for a power cell row x, where x=3L−2 for Lis integer and L=1 to the upper integer limit of$\left( \frac{k}{3} \right),$ the first switch midpoint receives thesecond phase voltage from an (av) secondary winding set, the secondswitch midpoint receives the third phase voltage from an (aw) secondarywinding set, and the capacitor midpoint receives the first phase voltagefrom an (au) secondary winding set, for a power cell row y, where y isinteger equals to x+1 and ranges from 2 to k, the first switch midpointreceives the third phase voltage from a (bw) secondary winding set, thesecond switch midpoint receives the first phase voltage from a (bu)secondary winding set, and the capacitor midpoint receives the secondphase voltage from a (bv) secondary winding set, and for a power cellrow z, where z is integer equals to x+2 and ranges from 3 to k, thefirst switch midpoint receives the first phase voltage from a (cu)secondary winding set, the second switch midpoint receives the secondphase voltage from a (cv) secondary winding set, and the capacitormidpoint receives the third phase voltage from a (cw) secondary windingset.
 10. The power supply of claim 9, wherein the power cells arecontrolled with sinusoidal pulse width modulation control signals, andcarrier angles θ₁, θ₂, and θ₃ for the rectifier in the power cells arephase shifted by 120 degrees.
 11. The power supply of claim 10, whereink=3 and the switching frequency is 1980 Hz.
 12. The power supply ofclaim 1, wherein the transformer comprises a primary winding, threepower cell sets, 3k secondary winding sets with no secondary phaseshifts between the secondary winding sets, each power cell set comprisesk power cells, and k is in integer.
 13. The power supply of claim 12,wherein for first power cells, the first switch midpoint receives thesecond phase voltage from an (av) secondary winding set, the secondswitch midpoint receives the third phase voltage from an (aw) secondarywinding set, and the capacitor midpoint receives the first phase voltagefrom an (au) secondary winding set, for second power cells, the firstswitch midpoint receives the third phase voltage from a (bw) secondarywinding set, the second switch midpoint receives the first phase voltagefrom a (bu) secondary winding set, and the capacitor midpoint receivesthe second phase voltage from a (bv) secondary winding set, and forthird power cells, the first switch midpoint receives the first phasevoltage from a (cu) secondary winding set, the second switch midpointreceives the second phase voltage from a (cv) secondary winding set, andthe capacitor midpoint receives the third phase voltage from a (cw)secondary winding set.
 14. The power supply of claim 13, wherein thepower cells are controlled with sinusoidal pulse width modulationcontrol signals, carrier angles θ_(n) for the rectifiers for each powercell row are the same, the carrier phase shifting angles θ₁, θ₂, . . . ,θ_(k) of the rectifiers in different power cell rows are shifted by$\frac{360}{k}$ degrees from each other.
 15. The power supply of claim14, wherein k=3, switching frequency is 1980 Hz, and the carrier anglesare θ₁ for the first power cell row, θ₂=θ₁±120° for the second powercell row, and θ₃=θ₁±240° for the third power cell row.
 16. The powersupply of claim 1, wherein a distribution of phase voltages at the firstswitch midpoint, the second switch midpoint, and the capacitor midpointreduces harmonics of a primary current harmonic spectrum.
 17. Anapparatus comprising: a transformer generating a plurality of firstphase voltages, a plurality of second phase voltages, and a plurality ofthird phase voltages; and a plurality of power cell sets that eachcomprise a plurality of power cells cascaded connected, wherein eachpower cell comprises a rectifier and an inverter, the rectifiercomprising two first active switches that are serially connected andreceive a phase voltage from a first secondary winding of a givensecondary winding set at a first switch midpoint, two second activeswitches that are serially connected and receive another phase voltagefrom a second secondary winding of the given winding set at a secondswitch midpoint, and two capacitors in parallel with the rectifier andthe inverter that are serially connected and receive another phasevoltage from a third secondary winding of the given secondary windingset at a capacitor midpoint between the capacitors, wherein the twofirst active switches, the two second active switches, and the twocapacitors of each power cell are connected in parallel.
 18. A methodcomprising: providing a transformer that receives a three-phase primaryvoltage and steps the three-phase primary voltage up or down to asecondary voltage with a plurality of secondary winding sets to aplurality of first phase voltages, a plurality of second phase voltages,and a plurality of third phase voltages; and providing a plurality ofpower cell sets that each comprise a plurality of power cells cascadedconnected, wherein each power cell comprises a rectifier and aninverter, the rectifier comprising two first active switches that areserially connected and receive a phase voltage from a first secondarywinding of a given secondary winding set at a first switch midpoint, twosecond active switches that are serially connected and receive anotherphase voltage from a second secondary winding of the given winding setat a second switch midpoint, and two capacitors in parallel with therectifier and the inverter that are serially connected and receiveanother phase voltage from a third secondary winding of the givensecondary winding set at a capacitor midpoint between the capacitors,wherein the two first active switches, the two second active switches,and the two capacitors of each power cell are connected in parallel. 19.A drive comprising: a motor; a power supply driving the motor, the powersupply comprising: a transformer that receives a three-phase primaryvoltage and steps the three-phase primary voltage up or down to asecondary voltage with a plurality of secondary winding sets to aplurality of first phase voltages, a plurality of second phase voltages,and a plurality of third phase voltages; and a plurality of power cellsets that each comprise a plurality of power cells cascaded connected,wherein each power cell comprises a rectifier and an inverter, therectifier comprising two first active switches that are seriallyconnected and receive a phase voltage from a first secondary winding ofa given secondary winding set at a first switch midpoint, two secondactive switches that are serially connected and receive another phasevoltage from a second secondary winding of the given winding set at asecond switch midpoint, and two capacitors in parallel with therectifier and the inverter that are serially connected and receiveanother phase voltage from a third secondary winding of the givensecondary winding set at a capacitor midpoint between the capacitors,wherein the two first active switches, the two second active switches,and the two capacitors of each power cell are connected in parallel.